Economies of scale. Flat screens were new-ish in the aughts. They were expensive things rich people had. Now that manufacturing processes have been refined and they can pump out millions a day, it's become significantly cheaper.

I remember when we got our first flat screen tv as a kid. 32" Tv (It was huge compared to the tube tv we had). It was over 500 dollars in the late 2000's for the cheapest model (Not sure exactly what year, probably like 2008-2009). Now you can get one for less than 200 dollars